242 DR. E. p. PHILLIPS 



the seeds formed by a single plant germinates and grows 

 to maturity the species is in no danger of extinction. 

 Some plants produce countless thousands of seeds as for 

 example the heaths and orchids so that in these cases 

 onl}' a small fraction per cent, need survive to carry on 

 the life of the species. 



In seed dispersal we must distinguish between (1) 

 occasional or accidental and (2) regular methods of 

 dispersal. In South x^frica we have examples of the 

 former during the summer-floods when seeds and fruits 

 of plants may be carried great distances from their 

 place of origin. It is by this means that some of the 

 noxious weeds are spread over the country. The 

 accidental dispersal of seeds throws light on many 

 questions of the geographical distribution of plants, such 

 as the planting of oceanic islands; the presence of stray 

 plants from one flora in the midst of an alien flora, 

 etc. Ocean currents often carry seeds and fruits long- 

 distances. The seeds of Entada scandens, an East 

 African leguminous plant, have been found on the shores 

 of Little Namaqualand and also on the beach near Cape 

 Town. We have records of seeds and fruits found on the 

 west coast of England which have been carried across 

 the Atlantic by the Gulf Stream. Many aquatic plants 

 are distributed by their seeds or fruits adhering in mud 

 to the feet of birds feeding on the banks of the river 

 or vlei. Human agency is to-day an important factor in 

 the accidental dispersal of seeds. We know only too well 

 the weeds which were imported into South Africa in 

 bales of forage from Australia and America during the 

 Boer War. Even small islands far removed from the 

 mainland are colonised by cosmo})olitan weeds in this 

 way. From Tristan d'Acunlia for instance the writer 

 recorded many temj)erate weeds which were not collected 

 by the riiallenger ILxpedition of ISTtMSTO. 



In the regular metliods of seed dispersal four agencies 

 are employed: 1. Wind. 2. Water. 3. Animals. 4. 

 Contraction of cofain tissiirs of the fruit. 



